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AR# 19865: Virtex-4 Configuration - IDCODE, verify, or other JTAG instruction failures on devices in a chain with Virtex-4 ES parts are due to TDO transitions on the rising edge of TCK as it exits SIR or SDR states (IEEE1149 compliance)

AR# 19865

Virtex-4 Configuration - IDCODE, verify, or other JTAG instruction failures on devices in a chain with Virtex-4 ES parts are due to TDO transitions on the rising edge of TCK as it exits SIR or SDR states (IEEE1149 compliance)

Description

IDCODE, verify, or other JTAG instruction failures on devices in a chain with Virtex-4 ES parts are due to TDO transitions on the rising edge of TCK as it exits SIR or SDR states.

Solution

TDO on Virtex-4 ES parts floats shortly after the rising edge of TCK on entry to the Exit1-IR or the Exit1-DR TAP state. The visible effect of this anomaly is that devices that have a hold time requirement of TDI exceeding 40 ns will incorrectly latch the final TDI value delivered from this device's TDO. This behavior can be mitigated by ensuring that this device is positioned next to a device in the boundary scan chain with a zero TDI hold time.